Red eye: what waits, and what does not

A red eye is one of the commonest reasons anyone consults about their eyes, and the great majority of cases are self-limiting. A small number are sight-threatening and need to be seen the same day. The useful thing is knowing which is which.

The dividing line

Two questions separate most of the serious from most of the minor.

Is the vision affected? Not "is it watery so things look smeary" — genuinely reduced, and still reduced after blinking.

Is there real pain? Not itching, not grittiness, not irritation. Deep, aching pain in or behind the eye.

If either answer is yes, it needs to be seen today. Add to that marked sensitivity to light, coloured haloes around lights, a pupil that looks different from the other one, or redness concentrated in a ring right around the cornea rather than spread across the white.

The common and minor

Viral conjunctivitis. Usually starts in one eye and moves to the other, watery discharge, gritty rather than painful, often with a cold or sore throat. It is highly contagious and runs its course over one to two weeks. Antibiotic drops do nothing for it. Cool compresses, lubricants, and strict hand hygiene — it spreads through households and schools very efficiently.

Bacterial conjunctivitis. Thicker, stickier discharge, lids gummed together in the morning. Frequently settles on its own; antibiotic drops shorten it. Contagious.

Allergic conjunctivitis. Both eyes, itching as the dominant symptom, often with sneezing or a blocked nose, worse in harmattan or with dust. Itching is the giveaway — infection irritates, allergy itches. Cool compresses and antihistamine drops help; rubbing makes it substantially worse.

Subconjunctival haemorrhage. A flat, bright red patch on the white of the eye, sharply defined, with no pain and no change in vision. It looks alarming and is harmless — a small vessel has bled under the surface, often after a cough, a sneeze, or nothing identifiable. It clears over a couple of weeks, changing colour like a bruise. Worth mentioning to a doctor if it recurs repeatedly, as it can relate to blood pressure or clotting.

Dry eye and blepharitis. Chronic low-grade redness, burning, crusted lid margins, worse at the end of the day.

The ones that need seeing today

Acute angle-closure glaucoma. Severe pain in and around one eye, blurred vision, coloured haloes around lights, a red eye, often nausea and vomiting. Frequently mistaken for a migraine or a stomach upset. Can destroy sight within a day or two.

Corneal ulcer or microbial keratitis. Pain, light sensitivity, reduced vision, sometimes a visible white spot on the cornea. Contact lens wearers are at substantially raised risk, particularly those who sleep in lenses or let water touch them. This scars, and scarring on the visual axis is permanent.

Uveitis. Inflammation inside the eye. Aching pain, marked light sensitivity, blurring, redness worst in a ring around the cornea. Needs prompt treatment and investigation.

Scleritis. Deep, boring pain, often waking the person at night, a deep violet-red rather than surface pink. Frequently associated with autoimmune disease.

Any red eye after an injury, especially where something may have entered the eye, or after grinding or hammering metal.

A red eye in a newborn in the first month, which needs urgent assessment.

What not to do

Do not use steroid drops that were not prescribed for this episode. In a viral corneal infection they can be catastrophic, and used casually they raise eye pressure and accelerate cataract.

Do not use whitening drops to make it look better. They constrict blood vessels, treat nothing, and produce rebound redness when stopped.

Do not put anything traditional or improvised into the eye. Breast milk, herbal preparations and sugar solutions all appear regularly in Lagos clinics attached to infections that were minor before the remedy.

Do not wear contact lenses through a red eye, and do not put the same pair back in afterwards.

If you are unsure, an optometrist can examine the eye under magnification and answer the question in a few minutes. That is a better use of an afternoon than waiting to see what happens.